Data-storing circular-disk media, such as optical or magnetic disks, have used either concentric or spiral tracks. Typically, so-called magnetic hard disks and flexible diskettes have used concentric tracks while optical disks have used a single spiral track on each disk. It has been a long felt need to provide disk media that has a maximal data-storage capacity and simple addressing. Several attempts at banding media into a plurality of different track lengths having different lineal and angular data densities have complicated the addressing so that it is cumbersome to manage.
Prior art disk media have track lengths keyed or based upon one disk revolution angular length, i.e. either one or more tracks are completely occupy one disk revolution (also termed tracks in the literature). Often disk revolutions are colloquially equated to tracks. Applicants have discovered that this constraint unduly limits the disk storage capacities and restricts flexibility in designing disk formats. In particular, formats for so-called banded disks for increased capacities have been limited to one track, an integral number of sectors, as well as tracks, per spiral track revolution. That is, track lengths are always tied to the length of a disk revolution. This discussion relates to addressable physical tracks on disk media. Such physical tracks should not be confused with so-called logical or virtual tracks which merely map data onto physical tracks of a disk medium.
Because addressable tracks in the prior art were coextensive with each spiral track revolution or one revolution of a concentric set of revolutions, the term track has been used to colloquially denote a revolution. As used herein, the term "addressable track" means an identifiable addressable entity that is separate and distinct from a revolution of a spiral track or one revolution of a disk having concentric revolutions. The term "revolution", as used herein, defines one circuit of a spiral track equal to 360.degree. of the spiral track. As applied to concentric revolutions, the term revolution means the entirety or 360.degree. of each such physical revolution. The term "addressable entity" is intended mean any addressable track, any one of a plurality of addressable sectors or records in each such addressable track. As will become apparent, the size and capacity of an addressable track is totally independent of the extent of a revolution.
It is a desire of disk manufacturers to comply with the American National Standards Institute (ANSI) and International Standards Organization (ISO) standards on interchange media, i.e. removable media. Such standards apply not only to magnetic tape, but also to removable data-storing disks. In particular, optical disks are the subject of pending, proposed and issued standards of ANSI and ISO. In making advances in the recording arts, it is also desirable for cost and marketing reasons to provide compatibility with existing standards and industry practices. This compatibility is often referred to as "backward compatibility".
Current interchange standards for optical disks, inter alia, provide for either 512 byte or 1024 byte data-storing sectors in a single spiral track of each disk medium. Each optical disk revolution, also termed a track in the prior art, contains either seventeen of the 1024 byte sectors or thirty-one of the 512 byte sectors. Combining the desires for greater disk capacity while maintaining linear addressing with backward compatibility creates substantial problems in the conflicting requirements.
The present invention solves both problems while providing a greater flexibility in designing, building and using data-storing disk media, drives and systems. A single base format enables using either the 512 or 1024 byte sectors without change in the base format; only the physical size of the sectors are changed. Other sector capacities may also be used in the single base format. The addressing methodology is unchanged, that is, the number of sectors in an addressable track is not changed. For 512 byte sectors there always are 31 sectors per addressable track and for 1024 byte sectors there are always 17 sectors per track.
It is also desired to directly access a data-storing area without extensive computation or scanning a disk being accessed. In banded disks, such direct accessing can be complicated and burdensome. Accordingly, addressing of tracks and sectors should be straight forward and consistent over the address space of the data-storing sectors and tracks. The sectors and tracks are addressable entities on a disk. Usually a single spiral track is not separately addressed, no limitation to that exclusion from addressing is intended. In accordance with the present invention, the addressable entities on a disk have data-storing capacities and angular extents that are independent of a data-storing capacity of one of the revolutions and of the angular extent of one revolution. That is, neither sectors nor addressable tracks need be and preferably are not selected to be an integral submultiple of a spiral track revolution nor an integral multiple of a spiral track revolution. In some embodiments there may be an integral number of sectors per revolution but not an integral number of addressable tracks per revolution nor does a single addressable track need to have an integral number of revolutions.